Curcumin downregulates the constitutive activity of NF-κB and induces apoptosis in novel mouse melanoma cells

Melanoma, the most deadly form of skin cancer, is very aggressive and resistant to present therapies. The transcription factor nuclear factor-kappa B (NF-κB) has been reported to be constitutively active in many types of cancer. Constitutively active NF-κB seen in melanoma likely plays a central role in cell survival and growth. We have established and characterized novel cell lines from our murine melanoma model. Here we report the constitutive activity of NF-κB in these melanoma-derived cells, as shown by electrophoretic mobility shift assay and reporter assays. We hypothesized that agents that inhibit NF-κB may also inhibit cell proliferation and may induce apoptosis in such melanoma cells. Curcumin has been shown to inhibit NF-κB activity in several cell types. In our system, curcumin selectively inhibited growth of melanoma cells, but not normal melanocytes. Curcumin induced melanoma cells to undergo apoptosis, as shown by caspase-3 activation, inversion of membrane phosphatidyl serine, and increases in cells in the sub-G1 phase. A curcumin dose-dependent inhibition of NF-κB-driven reporter activity correlated with decreased levels of phospho-IκBα, and decreased expression of NF-κB-target genes COX-2 and cyclin D1. This study demonstrates that the use of cells from our model system can facilitate studies of signaling pathways in melanoma. We furthermore conclude that curcumin, a natural and safe compound, inhibits NF-κB activity and the expression of its downstream target genes, and also selectively induces apoptosis of melanoma cells but not normal melanocytes. These encouraging in-vitro results support further investigation of curcumin for treatment of melanoma in vivo.